All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
According to the view of the majority of the scholars the 'Awrah (parts of the body that should be covered in Islam) of a woman in front of another Muslim woman is from the navel to the knee, as we clarified in Fatwa 84062.
Therefore, according to this opinion, it is permissible for a Muslim woman to see what is above the navel and below the knees of the body of another Muslim woman, like the breasts, the neck and legs below the knees. This is because women, being of the same sex, do not usually have any attraction to one another, but, if such desire is expected or feared (to develop), then exposing these parts becomes forbidden as confirmed by the scholars . This is the opinion we adopt here at Islamweb.
On the other hand, there are some scholars who hold the view that a Muslim woman may only see of another woman what a man may see from his female Mahaarim (plural of Mahram, i.e. a spouse [not included in this case] or a person whom one is permanently prohibited from marrying due to suckling, marital, or blood relations). This refers to what usually appears, like the hair, the upper chest close to the neck, the lower part of the legs below the knee. This does not include what is usually covered, like the belly, the breasts, the back, and the thighs (from the knee up).
As regards the wife of one's maternal uncle, she is like the wife of one's paternal uncle; she is not a Mahram. Therefore, it is not permissible to shake hands with the wife of one's maternal or paternal uncle, or the wife of one's brother, and it is also not permissible to stay in seclusion with any of them. Claiming that the wife of one's maternal uncle is a Mahram but not the wife of one's paternal uncle is wrong, unless there is an Islamic legal reason that changes the status of one's maternal uncle to a Mahram, like suckling or family lineage.
Allaah Knows best.